Dirt and deposits under the oil filler cap
Sometime you might open up an oil filler cap and you will see abnormal small deposits(emulsions) there. It often happens when we drive a cold engine during the winter time. Eventually, moisture that starts to get into the engine turns oil into light-beige emulsion.
When you are seeing dark-brown tarry deposits - this indicates a severe contamination of the engine oil system.
Change the oil and clean the oil system: VitaFlush – oil system cleaner need to be applied right after oil change(245-620 miles of run).
If such an occurrence is observed in winter and the problem disappears after the engine is warmed up, there is nothing to worry about, it is a normal process.